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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2189) HCM trashes meta cache even when not needed
Date Wed, 10 Feb 2010 18:24:31 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12832108#action_12832108
] 

Jean-Daniel Cryans commented on HBASE-2189:
-------------------------------------------

Seems I forgot to handle an exception, let's fix that.

> HCM trashes meta cache even when not needed
> -------------------------------------------
>
>                 Key: HBASE-2189
>                 URL: https://issues.apache.org/jira/browse/HBASE-2189
>             Project: Hadoop HBase
>          Issue Type: Improvement
>    Affects Versions: 0.20.3
>            Reporter: Jean-Daniel Cryans
>            Assignee: Jean-Daniel Cryans
>             Fix For: 0.20.4, 0.21.0
>
>         Attachments: HBASE-2189.patch
>
>
> I was investigating HBASE-2175 when I saw that we are doing a lot more ROOT lookups than
needed. For example, typical output of PE seqWrite during split:
> {code}
> client.HConnectionManager$TableServers: Removed TestTable,,1265524229864 for tableName=TestTable
from cache because of 0000380292
> client.HConnectionManager$TableServers: locateRegionInMeta attempt 0 of 10 failed; retrying
after sleep of 1000 because:
>  No server address listed in .META. for region TestTable,0000086976,1265524283534
> client.HConnectionManager$TableServers: Removed .META.,,1 for tableName=.META. from cache
because of TestTable,0000380292,99999999999999
> client.HConnectionManager$TableServers: Cached location for .META.,,1 is 192.168.1.103:56279
> client.HConnectionManager$TableServers: locateRegionInMeta attempt 1 of 10 failed; retrying
after sleep of 1000 because: 
>  No server address listed in .META. for region TestTable,0000086976,1265524283534
> client.HConnectionManager$TableServers: Removed .META.,,1 for tableName=.META. from cache
because of TestTable,0000380292,99999999999999
> client.HConnectionManager$TableServers: Cached location for .META.,,1 is 192.168.1.103:56279
> client.HConnectionManager$TableServers: Cached location for TestTable,0000086976,1265524283534
is 192.168.1.103:56279
> {code}
> So why exactly are we removing .META.,,1 from the cache? Because a row didn't have the
right address? So that means we did contact .META. but the information we got is still stall
because the split isn't finished yet... but why should that result in trashing the cache?

> Because we don't differentiate between NSRE / WRE from other exceptions like empty server
address. This happens a lot more often now that the Master clears that cell when a region
is closed instead of keeping the old value.

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